Error when a constant is used for Repeat transformation without Count

I have an integration with DataMapper which maps one array to another. For filling target field ("surname") which missing in the source array, I wanted to use constant. So I create a constant and map it to that target field with "Repeat" transformation and without any Count.

However, when I run integration, I see following error in the activity log:

io.atlasmap.api.AtlasException: Errors: [Failed to apply field action: Error processing action Repeat: Document='null(ID:DOC.Constants.26216)', path='/testName'], 
	at org.apache.camel.component.atlasmap.AtlasEndpoint.onExchange(AtlasEndpoint.java:239)
	at org.apache.camel.impl.ProcessorEndpoint$1.process(ProcessorEndpoint.java:71)
...

When I fill the count number, the error is gone. But, during the creating of mapping, I don't know how many objects will arrive from the source connection. I would expected that the count is not necessary in this case because the number of target objects is determined by the number of source objects in the array.

Is this a limitation of DataMapper (that the Count param need to be set when the source field is not a part of the array, or this affects only constant?) or a bug?

I would expected that when I am mapping only contant to a field of an array, the count must be set. But when another field from the source array is mapped to the target array, the count doesn't need to be set.

--------
The default postrgesql connection is used as a source (select * from todo)
AMQ step is used as a target with JSON instance
e.g.

{
  "officeNumber": 1,
  "arr": [
    {
      "name":"test1",
      "surname":"surname1",
      "addresses":[
        {
          "street":"street1"
        },
        {
          "street":"street2"
        }
      ]
    }
  ]
}